Bennett struggled to explain to interviewer Nick Ferrari how the Greens would pay for their housing policy. Ferrari appeared bemused by Bennett's estimates of how little each new home would cost. "What are they made of? Plywood?" he asked. His questions were met with frequent silences from Bennett, as well as coughing.

Ferrari was forced to ask at one point: "Are you alright?"

The Green Party leader's performance was met with horror by political reporters who could barely bring themselves to listen to the end.

Bennett's Tuesday morning interviews risk overshadowing the Green Party's campaign launch, as well as obscuring a ComRes poll in today's Daily Mail which gave the party its highest ever rating. The party's share of the vote has risen to 8 per cent – it's highest showing with ComRes since 2010. The poll puts them level with the Liberal Democrats.

Bennett later issued an apology to party members. Speaking later at a press conference to launch the party’s campaign, Bennett admitted it was “absolutely excruciating in the studio”. “Occasionally one has a mind blank,” she added.

Appearing later on the BBC Daily Politics, she issued an apology to party members, admitting she had not done "any kind of job" of presenting the policies.

"I had a very bad interview on housing this morning, I’m very happy to confess that and I’m very sorry to the Green party members who I didn’t do a good job, any kind of job of presenting our policies on," she said.